1. Field of the Invention
The invention relates to an arrangement for taking a signal sample from a radio frequency (RF) signal.
2. Description of the Related Art
In base stations of mobile networks, a sample of a transmission signal can be needed for testing purposes, for instance. A signal extraction can also be needed in the implementation of a mobile terminal locating service. The service can be based on triangular measurements, where the mobile terminal monitors pilot signals from at least three base stations. Locating of the terminal can be based on known information on exact locations of the base stations, receiving moments of the signals transmitted from different base stations, and transmission moments of the signals. To find out exact transmission moments of the signals at the base stations, an extraction of the transmission signals can be taken.
An extraction can be taken from a signal by a directional coupler, for instance. The directional coupler, however, is a costly solution and it has a certain resistance, thereby lowering the power of the signal from which the extraction is taken. Another solution for taking a sample of a signal is a radio frequency probe, which is injected into the transmission line.
Prior art solutions have the significant disadvantage that they are not suited for serial handling when signal samples are needed from more than one transmission line. For instance, in a base station, a signal sample is often needed from transmission lines that lead to different transmission antennas. In the prior art solutions, in order to jointly handle these signals, a sampler is needed for each transmission line and a combiner for combining the obtained samples.